This invention relates to thermostats for electric heating or cooling apparatus. The invention is discussed in connection with so-called line voltage thermostats, wherein the load current required by an electric heater or a room air conditioner is carried by the switch that forms part of the thermostat, but it applies equally to other thermostats of similar construction.
One type of line voltage thermostat includes an ambient temperature sensing bimetal formed of an elongated sheet or plate of sufficient width for rigidity. The bimetal is pivotally mounted near one end from a base plate and is oriented vertically when mounted on a wall of a room. An adjustment screw is screwed into a tapped hole in the mid section of the bimetal from the front, and the end of the screw bears against the spring-loaded plunger of a snap-switch. A rotatable cam bears against the bimetal element near the other end in opposition to the force exerted against the adjustment screw in the bimetal by the plunger and the spring of the switch.
The set-point temperature is determined by the rotational position of the cam of the thermostat and the thermostat is calibrated by turning the adjustment or calibration screw into or out of the bimetal element with the screw engaging against the plunger of the switch. It is usually desired to calibrate the thermostat so that the switch will be actuated when a pointer on the cam or on a knob affixed to it points upright or to a "normal" position when the temperature rises to approximately 70.degree. F. The adjustment of the calibrating screw is usually performed by the manufacturer and then locked or cemented against further rotation. More broadly stated, known thermostats generally include a temperature sensor, a set-point adjusting cam and a separate calibrating screw.